A British journalist held hostage by the Taliban in Pakistan's tribal belt for almost six months, has been released, the British high commission in Islamabad announced today.

"We can confirm that Asad Qureshi has been released and our consular team are providing him with assistance," a high commission spokesman said.

Qureshi was working for an independent production company on a documentary commissioned by Channel 4 when he was abducted in North Waziristan on 26 March. Also kidnapped were two retired Pakistani intelligence officers, one of whom, Khalid Khawaja, was subsequently beheaded.

The whereabouts of the other, Sultan Amir Tarar, are unknown. He was last seen in a hostage video released on 26 July.

Qureshi, who also has Pakistani nationality, reached Islamabad last night where he was reunited with his family and debriefed by British officials.

Sources close to negotiations said his release had been directly brokered by Qureshi's relatives.

The kidnappers had demanded a ransom of $10m (£6.5m) and the release of several Taliban prisoners in return for Qureshi. It was not clear whether any of their demands had been met.

The Guardian and other media organisations have not previously reported Qureshi's relationship with Channel 4, which the station feared would hinder efforts to secure his release.

In March, Qureshi seemed to be in good company when he travelled into the tribal belt with Khawaja and Tarar, a former ISI officer better known as "Colonel Imam", who were two of Pakistan's most prominent fundamentalist sympathisers.

The group's intermediary was "Usman Punjabi", a militant leader who promised access to the main Tehrik-i-Taliban group and its leader, Hakimullah Mehsud.

The US government, which accuses Mehsud of orchestrating a suicide attack on a CIA base in Afghanistan that killed seven spies last December, added him to its list of "specially designated global terrorists" on 1 September.

Khawaja and Tarar's militant links failed them, however, when they were kidnapped by a group calling itself Asian Tigers. Tribal sources said it was a front for Lashkar-e-Jhangvi, a vicious sectarian group that has developed strong links to the Taliban in recent years.

In April Khawaja appeared in a video, in which he claimed to have continuing links to the ISI and CIA and to have betrayed extremist militants during the 2007 Red Mosque siege in Islamabad. Khawaja was under clear pressure when making the statement.

Days later his body was found in a ditch near the town of Mir Ali in North Waziristan with a warning note to other "American spies".

The killing hastened efforts to free Qureshi and Imam by their relatives, Channel 4, the ISI and a delegation from the Jamiat Ulema-e-Islam religious party that held talks with the militants.

There were also unconfirmed approaches by Afghan Taliban to secure the release of Tarar, a legendary figure in Pakistani intelligence sometimes dubbed the "father of the Taliban" for his role in nurturing the militant movement in the 1990s, when he was an ISI officer stationed in western Afghanistan.

The Pakistani and Afghan Taliban are linked, but operate separately. Tarar was last seen pleading for his life in the July 26 video. At Tarar's home in Rawalpindi a woman who identified herself as his daughter said the family had "no idea" about his location or condition. "We still don't know. We have no contact with them," she said.